The present invention is directed to an improved control apparatus for control systems such as antiskid brake control systems.
Sophisticated control systems such as antiskid control systems often include three or more subsystems for generating intermediate control signals. For example, the antiskid control system shown in U.S. Pat. No. 3,724,916, issued Apr. 3, 1973 to Edgar A. Hirzel, is an analog control system which includes a modulator circuit for generating a first intermediate control signal as a time integral function of an input signal and a transient control circuit for generating a second intermediate control signal. In addition, it is a common practice to include lead circuits for generating another intermediate control signal as a function of a time derivative of wheel speed. Typically, these intermediate control signals are then combined to produce a composite control signal which is used to modify the action of the brake application means to reduce wheel skidding and optimize braking efficiency.
In the case of analog circuitry, it is generally possible for each of the subsystems for generating intermediate control signals to function in parallel. In this manner the time delay between the time when the input signal (usually wheel velocity) changes and the time when the composite control signal responds can be kept to an acceptable level.
However, when such control systems are implemented as programmed computers, problems of excessive delay times can result. One type of such a digital antiskid system utilizes a digital wheel speed sensor which posts a new value of the wheel speed at periodic intervals, such as two hundred times a second, for example. Because a computer operates in a serial rather than a parallel manner, excessive delays can result between the time the wheel signal is posted and the time the revised composite control signal is generated by the computer as a combination of the several intermediate control signals.